Television receiver



Nov. 25, 1941. J. c. WILSON TELEVISION RECEIVER Filed Sept. 5 0, 1940 0. WILSON BY 44 g INVENTOR JOHN ATTORNEY a v "62368 5.522% 05:58 25.1. d: wz zo=oz m O 0 Q m1 L 0% E r 6 2 .HI E z o o mwifm: E 52.322 5: E 5533mm 12.355 SzunSE .wwwfifiww 553mm. -85; b.5325; 992 0 0 U 6 Q ma Q s Q g oi O Y mzzs $5 555 56558 6 \uN M mm Patented Na. 25, 1941 TELEVISION RECEIVER John C. Wilson, Bayside, N. Y., assignor to Hazeltine Corporation, a corporation of Delaware Application September 30, 1940, Serial No. 358,988

9 Claims.

This invention relates generally to television receivers and, particularly, to a television receiver incorporating and arrangement for effectively preventing the reproduction of noise from the line-scanning oscillator of the receiver during periods when the oscillator is operative but during which no synchronizing signals are proparatus associated with the television receiver.

. Oscillations at thefield-scanning frequency ofvided therefor, due, for instance, to the fact that no television signal is being received.

It is customary to design a scanning oscillator of a television receiver normally to have-a frequency considerably below the frequency corre- 'sponding to that of the associatedscanningfield and to utilize synchronizing signals associated with the received television signal to increase and maintain the oscillator fre'quencyat the proper value. The natural frequency of such an oscillator ismade considerably lower than that of the associated scanning field for the reason that such i an oscillator usually comprises a discharge device, such as a vacuum tube, the operating potentials of which may vary considerably in use thereby varying its natural frequency. Inasmuch asit is necessary to utilize the synchronizing signals of a received television signal to increase the frequency of the scanning oscillator, it is, therefore, highly desirable to provide an oscillator for nor-. mally generating oscillations of a frequency considerably below that of the associated seaming field in order that the frequency of such normally generated oscillations will be lower than that conventional television signals, that is,- 60 cycles vper second, are not particularly troublesome due to the fact that suihcient energy at this latter frequency is not readily translated to portions of the system where such energy produces undesirable effects.

It is an object of the invention, therefore, to provide an improved television receiver by means of, which one or more of the above-mentioned disadvantages ofreceivers of the prior art may be eliminated.

It is a further object of the invention to provide a television receiver comprising a line-scanning oscillator the natural frequency of which is increased during periods when no television 1 signals are being received.

.It is a further object of the invention to provide a television receiver comprising a line-scanning oscillator having associated therewith apparatus for preventing noise from being generated at the normal natural oscillator frequency 1 during periods when no television signal is being received.

Iri accordance with the invention, a television receiver adapted to receive a television signal of the associated scanning field, and thus subject to synchronizing control under all normal conditions of operation. Thus, in the absence of a received television signal, the scanning oscillators of conventional television receivers run at considerably lower frequencies than those corresponding to the associated scanning fields when a television signal is being received. Conventionally, a line-scanning frequency of 13,230 cycles per second is utilized and the oscillator in such a receiver is usually designed to have a normal frequency in the vicinity of 10,000 cycles in the absence of a received television signal. Oscillations having a frequency of this order are particularly troublesome for the reason that this frequency is well within the audible range for most users and the frequency is one at which mechanical noise, due to the oscillations, can frequently be heard, even in the absence of a sound-reproducing system associated with the television receiver. Furthermore, oscillations having a frequency in this vicinity may also be particularly troublesome due to the fact that they are cross-coupled into the sound-reproducing antelevision signal.

including line-synchronizing components comprises a line-scanning oscillator, means responsive to a. received television signal for deriving a control effect, and means for utilizing the control effect for conditioning the oscillator to generate oscillations at a. frequency substantially less than the line-scanning frequency of a" television signal being received and for rendering such oscillations inaudible in the absence of a received The receiver also includes means for utilizing received line-synchronizing components for synchronizing the oscillator at the line-scanning frequency to develop a line. scanning field for the receiver.

In accordance with a preferred embodiment of the invention, a television receiver comprises a line-scanning oscillator normally having. a predetermined natural frequency for generating os the received signal to develop a line-scanning field for the receiver.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description 'taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Fig. 1 of the drawing is a circuit diagram, partly schematic, of a completev television receiver of the superheterodyne type embodying a line-scanning oscillator in accordance with the present invention; while Fig. 2 is 'a'circuit diagram of a modification of the portion of the circuit of Fig. 1 comprising the present invention.

Referring now more particularly to Fig. 1 of the drawing, the system represented comprises a receiver of the superheterodyne type including an antenna system l0, ll connected to a radiofrequency amplifier l2 to which is connected in cascade, in the order named, an oscillator-modulator ii, an intermediate-frequency amplifier l4, a detector IS, a video-frequency amplifier I4, and an image-reproducing device IT. A field-scanning oscillator I8 and a line-scanning oscillator I! are coupled to an output circuit of detector II through a synchronizing-signal separator 20, the field-scanning oscillator l3 and the line-scanning oscillator is being coupled to the field-deflecting windings 22, 23 and the line deflecting windings 24, 25, respectively, of the image-reproducing device H. A sound signal-translating channel 26 and associated loudspeaker 21 are coupled to an output circuit of intermediate-frequency amplifier l4 in order to translate and reproduce sound signals accompanying the received television pro-.

gram. The stages or units ill-21, inclusive, with the exception of unit l9, presently to be described, may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are deemed unnecessary herein.

Referring briefly, however, to the operation of the system described above, television signals intercepted by antenna circuit I 0, II are selected and amplified in radio-frequency amplifier I2 and coupled to the oscillator-modulator l3, wherein they are converted into intermediate-frequency signals which, in turn, are selectively amplified in the intermediate-frequency amplifier l4 and delivered to the detector ii. The modulation com- Referring now, more particularly, to the portion of the system of Fig. 1 embodying the present invention, unit l3 comprises a line-scanning oscillator of the E/L type comprising a vacuum tube 30 to the input electrodes of which linesynchronizing signals are applied through a coupling condenser 3|. The oscillator l9 comprises an inductance 33 in the anode circuit of tube 33 and an inductance 34 in the grid-cathode circuit of tube 30, the inductance 34 being regeneratively inductively coupled to inductance 33. A suitable normal bias is provided for vacuum tube by means of a cathode resistor 37! by-passedfor alternatingcurrents by condenser 38. An inductance 33 is connected in series with line-scanning coils 24, 25 and inductively coupled to inductance 33 in the anode circuit of tube 30.

In order to provide a suitable automatic amplification control source for the receiver, there In order to provide means responsive to a re-- ceived television signal for deriving a control effect and means for utilizing said control effect for ponents of the signal are derived by the detector l5 and are supplied to the video-frequency amplifier l8 wherein they are amplified and from which they are supplied, in the usual manner, to abrilliancy-control electrode of the image-reproducing device I 'I. Modulation components derived in detector I? are also supplied through synchronizing-signs separator 20 to the synchronizingcontro1 elements of field-scanning os-' cillator l8 and line-scanning oscillator IS. The intensity of the scanning ray of device I! is thus modulated or controlled in accordance with the video-signal voltages impressed'uponits control electrode in the usual manner. Scanning waves are generated by the field-scanning oscillator l3 and the line-scanning oscillator l9, which are controlled by synchronizing-voltage pulses su'pplied from detector l5 through synchronizingsignal separator 20, and applied to the scanning elements of the image-reproducing device ,I'! to reproduce electric scanning fields, thereby to defleet the scanning ray in two directions normal to each other so as to trace a rectilinear scanning pattern on the screen and thereby reconstruct the transmitted image.

decreasing the natural frequency of the linescanning oscillator of the system and for maintaining such natural frequency at a value substantially less than the line-scanning frequency of the television signal being received, the unidirectional voltage developed across resistor M is also utilized to supply a control bias for vacuum tube 30, being applied to the grid circuit thereof through a direct current amplifier 36.

In considering the operation of the system Just described, it will be seen that there is comprised in unit i 9 an oscillator of a conventional type,

the operation of which is described in detail, for

instance, in United States Letters Patent No. 2,118,977, granted May 31, 1938. Briefly, when the tube 30 becomes conductive, current flows through the inductance 33 and, since the resistance of the anode circuit is small and the reactance of inductance 33 is chosen to be high relative to the internal impedance of the tube 34, the current builds up through the inductance 33 substantially linearly with time. This increasing anode current causes a voltage to be fed back to the grid circuit of tube 30 so as to increase the potential of the grid thereof positively, still further increasing the conductivity of the tube, until current saturation in tube 30 is approached. At this time, the rate of increase of current begins to decrease and the potential of the grid of tube 30 also decreases actually reversing in polarity and building up negatively to an extent such that the tube can be operated to cutoff by a negative synchronizing pulse applied to its input electrode through condenser 3!. Upon the termination of the synchronising pulse, the tube 30 again becomes conductive and the cycle is repeated at the line-scanning frequency.

' The input potential at which vacuum tube 33 becomes conductive is, in the absence of a received television signal, dependent upon the bias provided by resistor 31. The circuit is so ad- 7 justed that, in the absence of a received teleunder the condition when a television signal is being received, it will be seen that a. negative bias, dependent in value upon the amplitude of the received carrier signal, is applied tovacuum tube 3| through the amplifier 3G whenever a television signal is being received so that the unidirectional potential developed across resistor 4| exceeds that developed across resistor 31.

The system is so adjusted that, under these conditions when triode 36 is conductive, the natural frequency of the line-scanning oscillator is decreased and maintained at a value substantially less than the line-scanning frequency of the system. As pointed out above in the preliminary portion of the specificationythis is the manner in which line-scanning oscillators areconven tionally designed and the received line-synchroinductance 52 until the negative potential of the control electrode of tube 50 is reduced to such a value that the tube will be rendered conductive upon a succeeding synchronizing pulse being applied to terminal C. The time constant of condenser 3|and resistor 53 is madeto be quite small relative to the time constant of the closed circuit including condenser 53 and resistors 54, 55, 58. The grid potential of tube 5G is also applied to tube 5|, whichcan be considered to be an amplifying tube, the condenser 51 performing the function of a wave-shaping element in the circuit.

In considering the operation of the circuit of Fig. 2 under the condition when diode 44 becomes nonconducting. it will be seen that the time constant of the grid circuit of tube 50 is thereby increased to decrease the natural frequency of the oscillator.. The circuit of Fig. 2, therefore, also comprises means responsiveto a received television signal for effectively decreasing the natural frequency of the oscillations of unit l9 to,

nizing pulses -are, therefore, effective to synchronize the scanning of the oscillator in the.

normal manner.

The embodiment illustrated in Fig. 21s substantially similar to unit l9 ofFig. 1 and circuit elements which are similar in the two figures have identical reference numerals. The unit IQ of Fig. 2 may be connected into the receiver of Hg. 1 by connecting the terminals of Fig; 2 to correspondingly-marked terminals of the receiver of Fig. 1 and substituting scanning plates for the windings 24, 25. The oscillator of Fig. 2 diflers from that of Fig. 1 primarily in the fact that a conventional type of blocking oscillator and maintaining it at, a value substantially less than the, line-scanning frequency of the television signal being received, together with means for utilizing line-synchronizing components derived from the received television signal and applied to terminal 0 of unit. I9 for synchronizing the oscillator at the Iine scanning frequency to develop a line-scanning field for the receiver. At

the same time, in the absence of a received television signaLthe natural frequency of the linescanning oscillator is sufliciently high to avoid reproduction of disturbing audible oscillations. specifically, in the circuit of Fig. 2, a control voltage is developed across resistor 4| and tube 44 is a biased unilaterally-conductive device through which the control voltage-is applied to 1 the oscillator to effect the desired control.

is utilized. This blocking oscillator of Fig. 2

comprises vacuum tubes Wand 5|. There is included in the input circuit of vacuum tube 5|] in series with-coupling condenser 3| a seriesconnected inductance 52, a condenser 53, and resistors El and 55. An inductance 56 is connected in the output circuit of tube '50 and inductively coupled to the inductance 52. The control electrode of vacuum tube 5| is connected directly to the control electrode 'of vacuum tube while there is included in the output circuit oi vacuum tube 5| a condenser 51 coupled across the output terminals D, E of the unit 19'. A resistor 58 is coupled between the common Junction of condenser 3| and inductance 52 and ground.

In considering the operation of the circuit of Fig. 2, and neglecting for the moment the function performed by the diode 4|, it will be seen that the circuit comprises a blocking oscillator of a conventional type and that, when a synchronizing signal is applied positively through condenser 3|, the condenser is immediately charged due to the small time constant of resister 58 and condenser 3|, and the control electrode of tube 50 is thereby rendered more positive to cause the tube 5|i to become conductive. The tube 50 is regenerated by the feed-back wing 58 and completes one-half cycle of oscillation at the natural frequency of the'grid circuit during which condenser 53 acquires a suf- While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and-modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within. the true spirit and scope of the invention.

What is claimed is:

1. A television receiver adapted to receive a television signal including line-synchronizing components and comprising,aline-scanningoscillator, means responsive to a received television signal for deriving a control effect, means for utilizing said control effect for conditioning said oscillator to generate oscillations at a frequency substantially less than the line-scanning 'fre-' quency of a television signal'beingreceiv'ed and for rendering said oscillations inaudible' in the absence of said received television signal, and means for utilizing said received line-synchronizing components for synchronizing said oscillator at said line-scanning frequency to develop a line-scanning field for said receiver.

2. A televisionreceiver adaptedtoreceive a television signal including line-synchronizing comv ponents and comprising,aline-scanningoscillator riving a control eflect, means for utilizing said ncient negative charge to block tube 50. The

condenser at then discharges slowly through the circuit inclug resistors 54, 65, and 58 and 'quency for generating oscillations, means responsive to a received television signal for decontrol eifect to decrease the natural frequency of said oscillator to, and maintain it at, a value substantially less than the line-scanning frequency of said television signal being received,

and means for utilizing said received line-synchronizing components for synchronizing said oscillator at said line-scanning frequency to designal for deriving a control effect, means for utilizing said control effect to decrease the natural frequency of said oscillator to, and maintain it at, a value substantially less than the linescanning frequency of said television signal being received, and means for utilizing said rechronizing said oscillator at said line-scanning frequency to develop a line-scanning field for said receiver.

4(A television receiver adapted to receive a television signal including line-synchronizing components and comprising, a line-scanning oscillator normally having a natural frequency greater than that which is audible at said receiver for generating oscillations, means responsive to a received television signal for deriving a control effect, means for utilizing said control effect to decrease the natural frequency of said osclllator to, and maintain it at, a value substantially less than the line-scanning frequency of trol source for deriving a control efiect, meats -ceived line-synchronizing components for synsaid television signal being received, and means for utilizing said received line-synchronizing components for synchronizing said oscillator at said line-scanning frequency to develop a linescanning field for said receiver.

5. A television receiver adapted to receive a television signal including line-synchronizing components and comprising, a line-scanning oscillator normally having a predetermined natural frequency for generating oscillations, means responsive to the amplitude of the received television signal for deriving a control effect, means for utilizing said control effect to decrease the natural frequency of said oscillator to, and maintain it at, a value substantially less than the linescanning frequency of said television signal being received, and means for utilizing said received line-synchronizing components for synchronizing said oscillator at said line-scanning frequency to develop a line-scanning field for said receiver.

6. A television receiver adapted to receive a television signal including line-synchronizing components and comprising, a line-scanning oscillator normally having a predetermined natural frequency for generating oscillations, means responsive to the amplitude of the carrier signal of the received television signal for deriving a tially less than the line-scanning frequency of said television signal being received, and means for utilizing said received line-synchronizingcomponents for synchronizing said oscillator at said line-scanning frequency to develop a linescanning field for said receiver.

7. A television receiver adapted to receive a television signal including line-synchronizing components and including an automatic amplification control, source comprising, a line-scanning oscillator normally having a predetermined natural frequency for generating oscillations, means responsive to-said, automatic amplification concomponents and comprising, a line-scanning oscillator normally having a predetermined natural frequency for generating oscillations, means responsive to a received signal for developing a bias voltage, means for utilizing said bias voltage for deriving a control efiect, means for utilizing said control effect to decrease the natural frequency of said oscillator to, and maintain it at, a value substantially less than the line-scanning frequency of said television signal being received, and means for utilizing said received line-synchronizing components for synchronizing said oscillator at said line-scanning frequency, to develop a line-scanning field for said receiver.

9. A television receiver adapted to receive a television signal including line-synchronizing components and comprising, a line-scanning oscillator normally having a predetermined natural frequency for generating oscillations, means responsive to a received signal for developing a control voltage, a biased unilaterally-conductive device, means for applying said control voltage to said oscillator through said device for decreasing the natural frequency of said oscillator to. and maintaining it at, a value substantially less than the line-scanning frequency of said television signal being received, and means for utilizing said received line-synchronizing components for syn- JOHN C. WILSON. 

